Implantable optical pressure sensor for sensing urinary sphincter pressure

ABSTRACT

The disclosure describes an optical fiber pressure sensor to measure sphincter pressure which may be incorporated into a therapeutic sphincter control system. The system senses sphincter pressure and sends the information to a stimulator that is capable of stimulation therapy to control sphincter contractility, thus reducing unwanted urinary incontinence. Measuring sphincter pressure is accomplished through the use of an optical fiber connected to flexible tube section placed through the sphincter, where properties of the emitted light are changed proportional to the pressure on the tube section. The light is returned to a light detector to measure light properties and create an electrical signal representative of the pressure on the tube section. The signal may then be sent by wireless telemetry to an implanted stimulator or external programmer.

RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 11/117,064, filed Apr.28, 2005, now allowed.

TECHNICAL FIELD

The invention relates to implantable medical devices and, moreparticularly, implantable sensors.

BACKGROUND

Urinary incontinence, or an inability to control urinary function, is acommon problem afflicting people of all ages, genders, and races.Various muscles, nerves, organs and conduits within the urinary tractcooperate to collect, store and release urine. A variety of disordersmay compromise urinary tract performance and contribute to incontinence.Many of the disorders may be associated with aging, injury or illness.

In some cases, urinary incontinence can be attributed to impropersphincter function, either in the internal urinary sphincter or externalurinary sphincter. For example, aging can often result in weakenedsphincter muscles, which causes incontinence. Some patients also maysuffer from nerve disorders that prevent proper triggering and operationof the bladder or sphincter muscles. Nerves running though the pelvicfloor stimulate contractility in the sphincter. A breakdown incommunication between the nervous system and the urinary sphincter canresult in urinary incontinence.

Electrical stimulation of nerves in the pelvic floor may provide aneffective therapy for a variety of disorders, including urinaryincontinence. For example, an implantable neurostimulator may beprovided to deliver electrical stimulation to the sacral nerve to inducesphincter constriction and thereby close or maintain closure of theurethra at the bladder neck. An appropriate course of neurostimulationtherapy may be aided by a sensor that monitors physiological conditionswith the urinary tract. In some cases, an implantable stimulation devicemay deliver stimulation therapy based on the level or state of a sensedphysiological condition.

SUMMARY

The invention is directed to an implantable optical pressure sensor forsensing urinary sphincter pressure, as well as a neurostimulation systemand method that make use of such a sensor for alleviation of urinaryincontinence. The sensor includes an optical fiber and a flexible tubesection. In some embodiments, the flexible tube section may contain areflective, flexible diaphragm. The tube section is deployed within thebladder neck to transduce urinary sphincter pressure as a function ofpressure exerted on the tube by the urinary sphincter. The optical fibertransmits light to the diaphragm, which reflects light back into theoptical fiber. The diaphragm deflects under pressure exerted on theflexible tube by the urinary sphincter. As a result, optical propertiesof the light reflected by the diaphragm change, indicating a change inurinary sphincter pressure.

Inadequate sphincter pressure may result in involuntary bladder voiding,i.e., incontinence. The optical pressure sensor may provide short- orlong-term monitoring of urinary sphincter pressure, e.g., for analysisby a clinician. Alternatively, the optical pressure sensor may form partof a closed-loop neurostimulation system. For example, neurostimulationtherapy can be applied to increase sphincter pressure, and therebyprevent involuntary urine leakage. In particular, an implantableneurostimulator may be responsive to urinary sphincter pressure signalsgenerated by the optical pressure sensor, as described herein, toprovide closed loop neurostimulation therapy to alleviate incontinence.

In one embodiment, the invention provides an implantable electricalstimulation system comprising an implantable pressure sensor includingan optical fiber, an emitter that transmits light via the optical fiber,a detector that detects reflected light via the optical fiber, circuitrythat generates pressure information based on the detected light, and afixation mechanism that positions the optical fiber proximate asphincter within a patient, and an implantable stimulator that deliverselectrical stimulation to the patient based on the pressure information.

In another embodiment, the invention provides a method comprisingtransmitting light via an optical fiber positioned proximate a sphincterwithin a patient, detecting reflected light via the optical fiber, andgenerating pressure information based on the detected light.

In an additional embodiment, the invention provides an implantablepressure sensor comprising an optical fiber, an emitter that transmitslight via the optical fiber, a detector that detects reflected light viathe optical fiber, circuitry that generates pressure information basedon the detected light, and a fixation mechanism that positions theoptical fiber proximate a sphincter within a patient.

In a further embodiment, the invention provides an implantable pressuresensor comprising a sensor housing, an optical fiber extending from thesensor housing, a flexible tube section coupled to the optical fiber, areflective, flexible diaphragm within the flexible tube section, anemitter that transmits light via the optical fiber to the diaphragm, adetector that detects reflected light from the diaphragm the opticalfiber, circuitry that generates pressure information based on thedetected light, and a fixation mechanism that positions the opticalfiber proximate a sphincter within a patient, wherein the diaphragmdeflects in response to exertion of pressure against the flexible tubesection by the sphincter.

Although the invention may be especially applicable to sensing urinarysphincter pressure, the invention alternatively may be applied moregenerally to other sphincters within the patient, such as the loweresophageal sphincter (LES) or pyloric sphincter. In addition, in thoseinstances, the invention may be adapted to support electricalstimulation of other body organs, such as the stomach or intestines,e.g., for treatment of obesity or gastric mobility disorders.

In various embodiments, the invention may provide one or moreadvantages. For example, the use of a thin, flexible optical pressuresensor permits pressure to be sensed within the narrow, constrictedpassage proximate the urinary sphincter. In this manner, pressure can besensed without significantly obstructing or altering the physiologicalfunction or the urinary sphincter.

The optical pressure sensor may be coupled to a larger sensor housingthat resides within the bladder and houses sensor electronics foremitting and detecting light to measure the pressure on the tube. Theoptical pressure sensor permits pressure information to be obtained on acontinuous or periodic basis as the patient goes about a daily routine.In addition, the flexible nature of the tube permits the sensor to beimplanted in a variety of locations, and to be constructed in variety ofshapes and sizes.

The optical pressure sensor may transmit sensed pressure information toan implantable stimulator to permit dynamic control of the therapydelivered by the stimulator on a closed-loop basis. For example, thestimulator may adjust stimulation parameters, such as amplitude, pulsewidth or pulse rate, in response to the sensed pressure. In this manner,the stimulator can provide enhanced efficacy and prevent involuntaryleakage. In addition, or alternatively, adjustment may involve on andoff cycling of the stimulation in response to pressure levels indicativeof a particular bladder fill stage. For example, stimulation may beturned off until the pressure level exceeds a threshold indicative of aparticular fill stage of the bladder. Also, with closed-loopstimulation, the stimulator may generate stimulation parameteradjustments that more effectively target the function of the urinarysphincter muscle, thereby enhancing stimulation efficacy. In somepatients, more effective stimulation via the sacral nerve may actuallyserve to strengthen the sphincter muscle, restoring proper operation.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an implantable stimulationsystem, incorporating urinary sphincter pressure sensor, for alleviationof urinary incontinence.

FIG. 2 is an enlarged schematic diagram illustrating an implantablepressure sensor with an optical tube extending through the urinarysphincter of a patient.

FIG. 3 is an enlarged, cross-sectional side view of the implantablepressure sensor of FIGS. 1 and 2.

FIG. 4 is a schematic diagram illustrating placement of an implantablepressure sensor with an optical tube extending through the internalurinary sphincter of a patient.

FIG. 5 is functional block diagram illustrating various components of anexemplary implantable pressure sensor.

FIG. 6 is a functional block diagram illustrating various components ofan implantable stimulator.

FIG. 7 is a schematic diagram illustrating cystoscopic deployment of animplantable pressure sensor via the urethra.

FIG. 8 is a schematic diagram illustrating retraction of a deploymentdevice upon fixation of a pressure sensor within a patient's urinarytract.

FIG. 9 is a cross-sectional side view of a deployment device duringdeployment and fixation of a pressure sensor.

FIG. 10 is a cross-sectional bottom view of the deployment device ofFIG. 10 before attachment of the pressure sensor.

FIG. 11 is a flow diagram illustrating a technique for delivery ofstimulation therapy based on closed loop feedback from an implantablepressure sensor.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram illustrating an implantable stimulationsystem 10 for alleviation of urinary incontinence. As shown in FIG. 1,system 10 includes an implantable optical pressure sensor 12,implantable stimulator 14 and external programmer 16 shown inconjunction with a patient 18. Pressure sensor 12 senses a pressurelevel exerted by urinary sphincter 22 on urethra 20 proximate the neck23 of bladder 24, and transmits pressure information based on the sensedpressure level to at least one of stimulator 14 and programmer 16 bywireless telemetry. Stimulator 14 or programmer 16 may record theinformation, generate adjustments to electrical stimulation parametersapplied by the stimulator, or both.

FIG. 2 is an enlarged schematic diagram illustrating implantable opticalpressure sensor 12. As shown in FIGS. 1 and 2, pressure sensor 12includes a sensor housing 26, an optical fiber 28, and a flexible tubesection 30. Flexible tube section 30 is positioned for engagement withurinary sphincter 22, and is sealed from the environment. Tube section30 contains a reflective, flexible diaphragm that deflects in responseto pressure changes within the tube section. Tube section 30 may befilled with air or other optically transmissive media. Optical fiber 28transmits light to the diaphragm and receives reflected light from thediaphragm. When the diaphragm deflects, the properties of the reflectedlight change, indicating a change in pressure within the flexible tubeand, in turn, a change in the pressure of urinary sphincter 22.

Sensor housing 26 contains a light emitter that transmits light throughoptical fiber 28 and a light detector that detects the reflected lightreceived from the optical fiber, as will be described in further detail.The light emitter and detector are positioned adjacent to a proximal endof optical fiber 28. If a single optical fiber is used for bothtransmission of light and reception of reflected light, an opticalcoupling element may be provided in sensor housing 26 to couple theemitter and detector to the optical fiber 28. In other embodiments,separate optical fibers can be used for transmission or reception. Ineither case, the light detector generates an output signal that variesaccording to the properties of the reflected light. Sensor housing 26further includes electronics to generate pressure information based onthe output signal, and telemetry circuitry for wireless transmission ofthe information to stimulator 14, programmer 16 or both.

As further shown in FIGS. 1 and 2, sensor housing 26 may reside withinbladder 24. Sensor housing 26 may be temporarily or permanently attachedto an inner wall 27 of bladder 24, such has the mucosal lining, as willbe described. Alternatively, housing 26 may be implanted sub-mucosally.Optical fiber 28 extends away from sensor housing 26 and through aninner lumen defined by the bladder neck proximate urinary sphincter 22.In this manner, flexible tube section 30 is positioned to directly sensethe pressure level exerted by urinary sphincter 22. Yet, optical fiber28 and tube section 30 may be sufficiently thin to avoid significantobstruction of urethra 20 or disruption of the function of urinarysphincter.

As a further alternative, housing 26 may reside outside bladder 24, inwhich case optical fiber 28 and tube section 30 may extend into bladder24 and through urinary sphincter 22 through a hole formed in thebladder. In this case, housing 26 may be surgically or laparoscopicallyimplanted within the abdomen. Fiber 28 and tube section 30 may besurgically or laparoscopically guided through a hole in the wall ofbladder 24. A cystoscope may be used to grab tube section 30 and pull itdownward through urinary sphincter 22 and urethra 20. In someembodiments, housing 26 and its contents may be integrated withstimulator 14, in which case optical fiber 28 and tube section 30extends from the stimulator housing and into bladder 24, much like leadscarrying stimulation or sense electrodes.

With further reference to FIG. 1, implantable stimulator 14 includes anelectrical lead 15 (partially shown in FIG. 1) carrying one or moreelectrodes that are placed at a nerve site within the pelvic floor. Forexample, the electrodes may be positioned to stimulate the sacral nerveand thereby innervate urinary sphincter 22. In particular, electricalstimulation may be applied to cause urinary sphincter 22 to increaseclosing pressure to avoid involuntary leakage from bladder 24.Alternatively, if voluntary voiding is desired by patient 18, electricalstimulation may be suspended or reduced to reduce the closing pressureexerted by urinary sphincter 22 on urethra 20 at the bladder neck.

For spinal cord injury patients who cannot perceive a sensation ofbladder fullness, sphincter pressure sensed by pressure sensor 12 may betransmitted to external programmer 16, with or without an accompanyingstimulator 14, to advise the patient when urinary sphincter pressure ishigh, indicating bladder fullness. In this case, the advice may be inthe form of a audible, visual or vibratory stimulus. In response to theadvice, the spinal cord injury patient is able to catheterize theurethra 20 and bladder 24 to voluntarily relieve urine.

Implantable stimulator 14 delivers stimulation therapy to the sacralnerve in order to keep the sphincter 22 constricted and keep contents ofbladder 24 from leaking out through urethra 20. At predetermined timesor at patient controlled instances, the external programmer 16 mayprogram stimulator 14 to interrupt the stimulation to allow thesphincter to relax, thus permitting voiding of bladder 24. Uponcompletion of the voiding event, external programmer 16 may programstimulator 14 to resume stimulation therapy and thereby maintain closureof urinary sphincter 22.

In addition, adjustment of stimulation parameters may be responsive topressure information transmitted by implantable optical pressure sensor12. For example, external programmer 16 or implantable stimulator 14 mayadjust stimulation parameters, such as amplitude, pulse width, and pulserate, based on pressure information received from implantable sensor 12.In this manner, implantable stimulator 14 adjusts stimulation to eitherincrease or reduce urinary sphincter pressure based on the actualpressure level exerted by urinary sphincter 22.

Pressure sensor 12 may transmit pressure information periodically, e.g.,every few seconds, minutes or hours. In some embodiments, pressuresensor 12 may transmit pressure information when there is an abruptchange in sphincter pressure, e.g., a pressure change that exceeds apredetermined threshold. In addition to parameter adjustments, oralternatively, adjustment may involve on and off cycling of thestimulation in response to pressure levels indicative of a particularbladder fill stage. For example, stimulation may be turned off until thepressure level exceeds a threshold indicative of a particular fill stageof the bladder, at which time stimulation is turned on. Then,stimulation parameters may be further adjusted as the sensed pressurelevel changes.

External programmer 16 may be a small, battery-powered, portable devicethat accompanies the patient 18 throughout a daily routine. Programmer16 may have a simple user interface, such as a button or keypad, and adisplay or lights. Patient 18 may initiate a voiding event, i.e., avoluntary voiding of bladder 24, via the user interface. In someembodiments, the length of time for a voiding event may be determined bypressing and holding down a button for the duration of a voiding event,pressing a button a first time to initiate voiding and a second timewhen voiding is complete, or by a predetermined length of time permittedby programmer 16 or implantable stimulator 14. In each case, programmer16 causes implantable stimulator 14 to temporarily terminate stimulationso that voluntary voiding is possible.

In some embodiments, stimulator 14 may immediately recommencestimulation upon completion of a voiding event, and thereafter adjuststimulation parameters based on pressure information generated byimplantable sensor 12. Alternatively, stimulator 14 may terminatestimulation upon initiation of a voiding event, and recommencestimulation only after implantable pressure sensor 12 measures adecrease of pressure in the urethra 20 that corresponds to bladder 24being empty. As a further alternative, following completion of thevoiding event, stimulator 14 may wait to recommence stimulation untilpressure sensor 12 detects generation of an inadequate pressure level byurinary sphincter 22, which could result in involuntary leakage. In thiscase, stimulator 14 recommences stimulation to enhance urinary sphincterpressure.

Implantable stimulator 14 may be constructed with a biocompatiblehousing, such as titanium or stainless steel, or a polymeric materialsuch as silicone or polyurethane, and surgically implanted at a site inpatient 18 near the pelvis. The implantation site may be a subcutaneouslocation in the side of the lower abdomen or the side of the lower back.One or more electrical stimulation leads 15 are connected to implantablestimulator 14 and surgically or percutaneously tunneled to place one ormore electrodes carried by a distal end of the lead at a desired nervesite, such as a sacral nerve site within the sacrum.

In the example of FIGS. 1 and 2, sensor housing 26 of implantablepressure sensor 12 is attached to the inner wall 27 of bladder 24 nearbladder neck 23. However, the attachment site for sensor housing 26could be anywhere with access to urinary sphincter 22. With a relativelylong optical fiber 28, for example, sensor housing 26 could bepositioned at a greater distance from bladder neck 23. Also, in someembodiments, sensor housing 26 could be attached within urethra 20,e.g., downstream from urinary sphincter 22, although attachment of thesensor housing within bladder 24 may be desirable to avoid obstructionof the urethra.

FIG. 3 is an enlarged, cross-sectional side view of the implantablepressure sensor 12 of FIGS. 1 and 2. As shown in FIG. 3, sensor housing26 receives the proximal end of flexible optical fiber 28. A sensingelement 34 is mounted within sensor housing 26 to sense a urinarysphincter pressure level via optical fiber 28. Sensing element 34 may becoupled to a circuit board 38 within sensor housing 26, and includes anoptical emitter 35 and a detector 37. Optical emitter 35 may be a lightemitting diode (LED). Detector 37 may be a photodiode. In the example ofFIG. 3, optical fiber 28 includes two optical fibers, i.e., a transmitfiber 39 coupled to emitter 35 and a receive fiber 41 coupled to opticaldetector 41. Each optical fiber 39, 41 extends into flexible tubesection 30.

Sensor housing 26 may be made from a biocompatible material such astitanium, stainless steel or nitinol, or a polymeric material such assilicone or polyurethane. Another material for fabrication of sensorhousing 26 is a two-part epoxy. An example of a suitable epoxy is atwo-part medical implant epoxy manufactured by Epoxy Technology, Inc.,mixed in a ratio of 10 grams of resin to one gram of activator. Ingeneral, sensor housing 26 contains no external openings, with theexception of the opening to receive optical fiber 28, thereby protectingsensing element 26 and circuit board 38 from the environment withinbladder 24. The proximal end of optical fiber 28 resides within sensorhousing 26 while the distal end resides outside of the sensor housing.The opening in sensor housing 26 that receives the proximal end ofoptical fiber 28 may be sealed to prevent exposure of interiorcomponents.

The core and cladding of optical fiber 28 may be formed from any of avariety of conventional glass or polymeric materials. In addition,single mode or multi-mode fibers may be selected. In some embodiments, aprotective, a flexible sheath (not shown) may be formed over opticalfiber 28. The flexibility of optical fiber 28 permits it to bend andconform to contours within bladder neck 23, facilitating placement offlexible tube section 30 within urethra 20 proximate urinary sphincter22.

Flexible tube section 30 may be formed from any of a variety offlexible, biocompatible materials such as polyurethane or silicone. Thematerial should be sufficiently flexible to permit deform in response topressure exerted on urethra 20 by urinary sphincter 22 at bladder neck23. Flexible tube section 30 preferably is sealed to define acompartment, so that deformation produces volumetric changes andpressure changes within the compartment. Accordingly, flexible tubesection 30 may have a closed distal end and a sealed proximal end thatis sealed about fiber 28. The compartment may contain a gaseous mediumsuch as air. During operation, urinary sphincter 22 exerts pressureinward against the outer wall of urethra 20. In turn, the inner wall ofurethra 20 exerts pressure inward against the outer wall of flexibletube section 30, causing the wall of the tube section to deform andcompress inward. In some embodiments, flexible tube section 30 may becoated to avoid calcification.

Inward deformation of flexible tube section 30 causes a mechanicaldeflection of the membrane mounted inside. As light is transmitted ontothe membrane by optical fiber 39, some of the reflected light receivedby optical fiber 41 is refracted to a varying degree based upon thedeformation of the membrane. When the reflected light is detected bylight detector 37, the light detector generates an output signal that isinfluenced by the physical properties of the detected light. Circuitrywithin sensing element generates pressure information based on thereflected light detected by detector 37.

The physical property may be simply an intensity of the received light,which is influenced by the degree of deflection of the membrane. In thiscase, an increase or decrease in the intensity of reflected light can beuse to produce a urinary sphincter pressure level. Alternatively,physical property may be a wavelength of the reflected light, relativeto a wavelength of the transmitted light. As the membrane deflects,changes in the wavelength of the reflected light can be used to producea urinary sphincter pressure level. In other embodiments, the membranemay be formed with an interference pattern or grating that aids inwavelength differentiation between the reflected light and thetransmitted light. Based upon the differences in amplitude, wavelength,or other optical properties, sensing element 34 generates a pressuresignal that represents the pressure on flexible tube section 30.Electronics on circuit board 38 generate pressure information based onthe pressure signal.

Optical fiber 28 and flexible tube section 30 may be provided withdifferent dimensions selected for patients having different anatomicaldimensions. In particular, implantable pressure sensor 12 may beconstructed with an optical fiber 28 and flexible tube section 30 havingdifferent lengths and diameters. Different tube lengths may be necessarygiven the distance between the attachment site of sensor housing 26 andurinary sphincter 22, either to ensure that flexible tube section 30reaches the sphincter or does not extend too far down urethra 20.Multiple diameters may also be necessary to allow a dysfunctionalsphincter 22 to close completely or to allow optical fiber 28 andflexible tube section 30 to be placed into a narrow urethra 20. Thedimensions may be fixed for a given pressure sensor 12, as a completeassembly. Alternatively, fluid tubes of different sizes may be attachedto a pressure sensor housing 26 by a physician prior to implantation.

In general, for male patients, optical fiber 28 and tube section 30 mayhave a combined length of less than approximately 9 cm and morepreferably less than approximately 7 cm. For female patients, opticalfiber 28 and tube section 30 may have a combined length of less thanapproximately 7 cm and more preferably less than approximately 5 cm. Insome embodiments, optical fiber 28 and tube section 30 may have acombined length of approximately 0.5 cm to 3 cm. The length of opticalfiber 28 and tube section 30 may vary according to the anatomy of thepatient, and may vary between male, female and pediatric patients. Inaddition, tube 30 may have an outer diameter in a range of approximately1 to 3 mm. The wall of tube 30 may be relatively thin to ensuresufficient deformation and conformability, yet thick enough to ensurestructural integrity. As an example, the thickness of the wall of tube30 may be in a range of approximately 0.1 mm to 0.3 mm.

Attaching implantable pressure sensor 12 to the mucosal lining ofbladder 24 may be accomplished in a variety of ways, but preferably iscompleted in a manner that will not excessively injure bladder 24.Preferably, attachment should cause limited inflammation no adversephysiological modification, such as tissue infection or a loss instructural integrity of bladder 24. However, it is desirable thatimplantable pressure sensor 12 also be attached securely to theattachment site in order to provide an extended period of measurementwithout prematurely loosening or detaching from the intended location.

As an example, sensor housing 26 may contain a vacuum cavity 39 thatpermits a vacuum to be drawn by a vacuum channel 40. The vacuum iscreated by a deployment device having a vacuum line in communicationwith vacuum channel 40. The vacuum draws a portion 42 of the mucosallining 44 of bladder 24 into vacuum cavity 39. Once the portion 42 ofmucosal lining 44 is captured within vacuum cavity 39, a fastening pin46 is driven into the captured tissue to attach sensor housing 26 withinbladder 24. Fastening pin 46 may be made from, for example, stainlesssteel, titanium, nitinol, or a high density polymer. The shaft of pin 46may be smooth or rough, and the tip may be a sharp point to allow foreasy penetration into tissue. Fastening pin 46 may be driven intohousing 26 and the portion 42 of mucosal lining 44 under pressure, orupon actuation by a push rod, administered by a deployment device.

In some embodiments, fastening pin 46 may be manufactured from adegradable material that the breaks down over time, e.g. in the presenceof urine, to release implantable pressure sensor 12 within a desiredtime period after attachment. In still another embodiment, implantablepressure sensor 12 may be attached without the use of a penetrating rodbut with a spring-loaded clip to pinch trapped mucosal lining 44 withincavity 39. A variety of other attachment mechanisms, such as pins,clips, barbs, sutures, helical screws, surgical adhesives, and the likemay be used to attach sensor housing 26 to mucosal lining 44 of bladder24.

FIG. 4 is a schematic diagram illustrating placement of an implantablepressure sensor 12 with a flexible optical fiber 28 extending throughthe urinary sphincter 22 of a patient 18. FIG. 4 also illustratesflexible tube section 30 in greater detail. In the example of FIG. 4,optical fiber 28, including transmit fiber 39 and receive fiber 41,leaves bladder 24 through bladder neck 23 and passes through internalurinary sphincter 22 as it enters urethra 20. In general, sphincter 22is an annulus shaped muscle that surrounds the portion of urethra 20below bladder neck 23 and constricts to make the urethral walls meet andthereby close urethra 20 to prevent involuntary urine leakage frombladder 24. Upon constriction of sphincter 22, the walls of urethra 20close onto flexible tube section 30 of optical fiber 28 to increase theinternal pressure of the tube section, which provides a measurement ofthe closing pressure of sphincter 22.

As further shown in FIG. 4, flexible diaphragm 43 is mounted withinflexible tube section 30 below optical fibers 39, 41. Flexible diaphragm43 includes an optically reflective surface on a side facing opticalfibers 39, 41. In this manner, light transmitted via optical fiber 39 isreflected by diaphragm 43 and received via optical fiber 41. Flexiblediaphragm may be substantially circular and bonded at its edges to aninner wall of flexible tube section 30. For example, flexible diaphragmmay be bonded to the inner wall of flexible tube section 30 byadhesives, ultrasonic welding, or other techniques. In some embodiments,tube section 30 may include an annular mounting ledge or otherequivalent mounting structures to support at least an outer edge of thediaphragm 43. Flexible diaphragm 43 may be formed from any of a varietyof flexible materials. The materials may be reflective. Alternatively, areflective coating may be formed on diaphragm 43, e.g., by vapordeposition, sputtering, dip coating, roll coating or the like.

Because optical fiber 28 and flexible tube section 30 have circularcross-sections and a small diameter, a closed sphincter 22 will still beable to substantially seal urethra 20 around optical fiber 28, flexibletube section 30, or both. When sphincter 22 is relaxed, in someembodiments, implantable pressure sensor 12 may be used to measure thepressure of fluid in urethra 20. The open sphincter 22 allows urine tobe passed out of the urethra and patient 18. Optical fiber 28 is underthe same pressure as the urethra and can allow implantable pressuresensor 12 to measure this urethral pressure. This may allow monitoringof urinary dysfunctions due to pressure during voiding events and mayalso be used by implantable stimulator 14 to detect the end of a voidingevent by measuring decrease of urethral pressure as an indication ofreduced urine flow.

As shown in FIG. 4, the placement of optical fiber 28 and flexible tubesection 30 does not significantly interfere with normal bladderfunction. Bladder function is unimpaired and fluid flow to urethra 20can occur normally, as flexible tube section 30 allows enough room forurine to pass and exit bladder 24 via urethra 20. Due to varying sizesand shapes of patient anatomy, optical fiber 28 and flexible tubesection 30 may be manufactured in a variety of lengths and diameters.

FIG. 5 is functional block diagram illustrating various components of anexemplary implantable pressure sensor 12. In the example of FIG. 5,implantable pressure sensor 12 includes a sensing element 34, processor48, memory 50, telemetry interface 52, and power source 54. Sensingelement 34 transforms measured changes in emitted light from opticalfiber 28 into electrical signals representative of closing pressure ofurinary sphincter 22. Again, optical fiber 28 may include a transmitfiber 39 and a receive fiber 41, or a single fiber with an opticalcoupler for optical coupling to emitter 35 and detector 37. Theelectrical signals may be amplified, filtered, and otherwise processedas appropriate by electronics within sensor 12. In particular, sensor 12may include circuitry to detect changes in light intensity orwavelength. In some embodiments, the signals may be converted to digitalvalues and processed by processor 48 before being saved to memory 50 orsent to implantable stimulator 14 as pressure information via telemetryinterface 52.

Memory 50 stores instructions for execution by processor 48 and pressureinformation generated by sensing element 36. Pressure data may then besent to implantable stimulator 14 or external programmer 16 forlong-term storage and retrieval by a user. Memory 50 may includeseparate memories for storing instructions and pressure information. Inaddition, processor 48 and memory 50 may implement loop recorderfunctionality in which processor 48 overwrites the oldest contentswithin the memory with new data as storage limits are met, therebyconserving memory space.

Processor 48 controls telemetry interface 52 to send pressureinformation to implantable stimulator 14 or programmer 16 on acontinuous basis, at periodic intervals, or upon request from theimplantable stimulator or programmer. Wireless telemetry may beaccomplished by radio frequency (RF) communication or proximal inductiveinteraction of pressure sensor 12 with programmer 16.

Power source 54 delivers operating power to the components ofimplantable pressure sensor 12. Power source 54 may include a batteryand a power generation circuit to produce the operating power. In someembodiments, the battery may be rechargeable to allow extended operationRecharging may be accomplished through proximal inductive interactionbetween an external charger and an inductive charging coil within sensor12. In some embodiments, power requirements may be small enough to allowsensor 12 to utilize patient motion and implement a kineticenergy-scavenging device to trickle charge a rechargeable battery. Inother embodiments, traditional batteries may be used for a limitedperiod of time. As a further alternative, an external inductive powersupply could transcutaneously power sensor 12 whenever pressuremeasurements are needed or desired.

FIG. 6 is a functional block diagram illustrating various components ofan implantable stimulator 14. In the example of FIG. 6, stimulator 14includes a processor 56, memory 58, stimulation pulse generator 60,telemetry interface 62, and power source 64. Memory 58 storesinstructions for execution by processor 56, stimulation therapy data,and pressure information received from pressure sensor 12 via telemetryinterface. Pressure information is received from pressure sensor 12 andmay be recorded for long-term storage and retrieval by a user, oradjustment of stimulation parameters, such as amplitude, pulse width orpulse rate. Memory 58 may include separate memories for storinginstructions, stimulation parameter sets, and pressure information.Processor 56 controls stimulation pulse generator 60 to deliverelectrical stimulation therapy and telemetry interface 62 to send andreceive information. An exemplary range of neurostimulation stimulationpulse parameters likely to be effective in treating incontinence, e.g.,when applied to the sacral or pudendal nerves, are as follows:

1. Frequency: between approximately 0.5 Hz and 500 Hz, more preferablybetween approximately 5 Hz and 250 Hz, and still more preferably betweenapproximately 10 Hz and 50 Hz.

2. Amplitude: between approximately 0.1 volts and 50 volts, morepreferably between approximately 0.5 volts and 20 volts, and still morepreferably between approximately 1 volt and 10 volts.

3. Pulse Width: between about 10 microseconds and 5000 microseconds,more preferably between approximately 100 microseconds and 1000microseconds, and still more preferably between approximately 180microseconds and 450 microseconds.

Based on pressure information received from sensor 12, processor 56interprets the information and determines whether any therapy parameteradjustments should be made. For example, processor 56 may compare thepressure level to one or more thresholds, and then take action to adjuststimulation parameters based on the pressure level. Information may bereceived from sensor 12 on a continuous basis, at periodic intervals, orupon request from stimulator 14 or external programmer 16.Alternatively, or additionally, pressure sensor 12 may transmit pressureinformation when there is an abrupt change in the pressure level, e.g.,at the onset of involuntary leakage.

In addition, processor 56 modifies parameter values stored in memory 58in response to pressure information from sensor 12, either independentlyor in response to programming changes from external programmer 16.Stimulation pulse generator 60 provides electrical stimulation accordingto the stored parameter values via a lead 15 implanted proximate to anerve, such as a sacral nerve. Processor 56 determines any parameteradjustments based on the pressure information obtained form sensor 12,and loads the adjustments into memory 58 for use in delivery ofstimulation.

As an example, if the pressure information indicates an inadequatesphincter closing pressure, processor 56 may increase the amplitude,pulse width or pulse rate of the electrical stimulation applied bystimulation pulse generator 60 to increase stimulation intensity, andthereby increase sphincter closing pressure. If sphincter closingpressure is adequate, processor 56 may implement a cycle of downwardadjustments in stimulation intensity until sphincter closing pressurebecomes inadequate, and then incrementally increase the stimulationupward until closing pressure is again adequate. In this way, processor56 converges toward an optimum level of stimulation. Although processor56 is described in this example as adjusting stimulation parameters, itis noted that the adjustments may be generated by external programmer16.

The adequacy of closing pressure is determined by reference to thepressure information obtained from sensor 12. Sphincter pressure maychange due to a variety of factors, such as an activity type, activitylevel or posture of the patient 18. Hence, for a given set ofstimulation parameters, the efficacy of stimulation may vary in terms ofsphincter pressure, due to changes in the physiological condition of thepatient. For this reason, the continuous or periodic availability ofpressure information from implantable sensor 12 is highly desirable.

With this pressure information, stimulator 14 is able to respond tochanges in sphincter pressure with dynamic adjustments in thestimulation parameters delivered to the patient 18. In particular,processor 56 is able to adjustment parameters in order to causeconstriction of sphincter 22 and thereby avoid involuntary leakage. Insome cases, the adjustment may be nearly instantaneous, yet preventleakage. As an example, if patient 18 laughs, coughs, or bends over, theresulted force on bladder 24 could overcome the closing pressure ofurinary sphincter 22. If pressure sensor 12 indicates an abrupt changein sphincter pressure, however, stimulator 14 can quickly respond bymore vigorously stimulating the sacral nerves to increase sphincterclosing pressure.

In general, if sphincter 22 is not constricting enough to effectivelyclose urethra 20, processor 56 may dynamically increase the level oftherapy to be delivered. Conversely, if sphincter 22 is consistentlyachieving effective constriction, processor 56 may incrementally reducestimulation, e.g., to conserve power resources.

As in the case of sensor 12, wireless telemetry in stimulator 14 may beaccomplished by radio frequency (RF) communication or proximal inductiveinteraction of pressure stimulator 14 with implantable pressure sensor12 or external programmer 16. Accordingly, telemetry interface 62 may besimilar to telemetry interface 52. Also, power source 64 of stimulator14 may be constructed somewhat similarly to power source 54. Forexample, power source 64 may be a rechargeable or non-rechargeablebattery, or alternatively take the form of a transcutaneous inductivepower interface.

FIG. 7 is a schematic diagram illustrating cystoscopic deployment of animplantable pressure sensor 12 via the urethra 20 using a deploymentdevice 66. Pressure sensor 12 may be surgically implanted. However,cystoscopic implantation via urethra is generally more desirable interms of patient trauma, recovery time, and infection risk. In theexample of FIG. 7, deployment device 66 includes a distal head 68, adelivery sheath 69 and a control handle 70. Deployment device 66 may bemanufactured from disposable materials for single use applications ormore durable materials for multiple applications capable of withstandingsterilization between patients.

As shown in FIG. 7, distal head 68 includes a cavity that retains sensorhousing 26 of implantable pressure sensor 12 for delivery to a desiredattachment site within bladder 24. Sensor housing 26 may be held withincavity 72 by a friction fit, vacuum pressure, or a mechanicalattachment. In each case, once distal head 68 reaches the attachmentsite, sensor housing 26 may be detached. Sheath 69 is attached to distalhead 68 and is steerable to navigate urethra 20 and guide the distalhead into position. In some embodiments, sheath 69 and distal head 68may include cystoscopic viewing components to permit visualization ofthe attachment site. In other cases, external visualization techniquessuch as ultrasound may be used. Sheath 68 may include one or moresteering mechanisms, such as wires, shape memory components, or thelike, to permit the distal region adjacent distal head 68 to turnabruptly for access to the mucosal lining of bladder 24.

A control handle 70 is attached to sheath 69 to aid the physician inmanually maneuvering deployment device 66 throughout urethra 20 andbladder 24. Control handle 70 may have a one or more controls thatenable the physician to contort sheath 69 and allow for deploymentdevice 66 to attach pressure sensor housing 26 to the mucosal lining ofbladder 24 and then release the sensor housing to complete implantation.A vacuum source 74 supplies negative pressure to a vacuum line withinsheath 69 to draw tissue into the vacuum cavity defined by sensorhousing 66. A positive pressure source 76 supplies positive pressure toa drive a fastening pin into the tissue captured in the vacuum cavity.

Deployment device 66 enters patient urethra 20 to deliver pressuresensor 12 and implant it within bladder 24. First, the physician mustguide distal head 68 through the opening of urethra 20 in patient 18.Second, distal head 68 continues to glide up urethra 20 and past therelaxed internal sphincter 22. Distal head 300 is then pushed throughbladder neck 23 and into bladder 24, for access to an appropriate siteto attach pressure sensor 12. Using actuators built into control handle70, sheath 69 is bent to angle distal head 68 into position. Again,sheath 69 may be steered using control wires, shape memory alloys or thelike.

As pressure sensor 12 is guided into place against the mucosal wall 44of bladder 24, a physician actuates control handle 70 to attach sensor12 to mucosal wall 44 and then release the attached sensor. Uponattachment, pressure sensor 12 is implanted within bladder 24 of patient18 and deployment device 66 is free to exit the bladder. Exemplarymethods for attachment and release of sensor 12, including the use ofboth vacuum pressure and positive pressure, will be described in greaterdetail below. Although FIG. 7 depicts cystoscopic deployment of pressuresensor 12, surgical or laparoscopic implantation techniquesalternatively may be used.

FIG. 8 is a schematic diagram illustrating retraction of deploymentdevice 66 upon fixation of pressure sensor 12 within the urinary tractof patient 18. Once the sensor 12 is released, optical fiber 28 remainsattached to sensor housing 26. During removal of deployment device 66,optical fiber 28 and flexible tube section 30 maintain position withinbladder neck 23 adjacent sphincter 22. As deployment device 66 isremoved, optical fiber 28 and flexible tube section 30 pass through aguide channel formed in the deployment device. The guide channel ensuresthat optical fiber 28 and flexible tube section 30 remain pinned betweendistal head 68 and the wall of bladder 24.

As distal head 68 slides through sphincter 22 and urethra 20, however,optical fiber 28 releases from deployment device 66 and is left in placewithin the urethra in the region proximate urinary sphincter 22.Deployment device 66 may then be completely withdrawn past the externalurinary sphincter and out of the remainder of urethra 20. In the exampleof FIG. 8, optical fiber 28 is suspended by device housing 26, which isattached to mucosal wall 44, and is held in place by pressure exertedagainst the urethral wall by urinary sphincter 22. In other embodiments,optical fiber 28 and flexible tube section 30 may be kept in place usingother techniques such as actively fixing optical fiber 28 or tubesection 30 to the side of urethra 20, e.g., with sutures or other anchormechanisms.

In a preferred embodiment, sheath 69 and distal head 68 may bedisposable. Disposable devices that come into contact with patient 18tissues and fluids greatly decrease the possibility of infection inimplantable devices. Control handle 70 does not come into contact withbody fluids of patient 18 and may be used for multiple patients. Inanother embodiment, the entire deployment device 66 may be manufacturedout of robust materials intended for multiple uses. The device wouldthen need to be sterilizable between uses. In still a furtherembodiment, the features of distal head 68 may be incorporated intopressure sensor 12. In this configuration, pressure sensor 12 may belarger in size but would include the necessary elements for attachmentwithin the device. After attachment, the entire sensor would detach fromsheath 69, making removal of deployment device 66 easier on patient 18.

After the useful life of implantable pressure sensor 12 is complete orit is no longer needed within patient 18, it can be removed from patient18 in some manner. As an example, deployment device 66 may be reinsertedinto patient 18, navigated into bladder 24, and reattached to pressuresensor 12. Deployment device 66 may then be withdrawn from the bladder24 and urethra 20, explanting sensor 12, including housing 26 andoptical fiber 28, from patient 18. In another embodiment, as mentionedwith respect to FIG. 3, the attachment method of pressure sensor 12 tobladder 24 may involve degradable materials, such as a biodegradablefixation pin. After a certain period of time exposed to urine in thebladder 24, the fixation material may structurally degrade and allowpressure sensor 12 to be released from the mucosal wall 44 of bladder24. In some embodiments, sensor 12 may be sized sufficiently small tofollow urine out of the bladder, urethra, and body during a voidingevent. In other embodiments, sensor housing 26 or tube section 30 maycarry a suture-like loop that can be hooked by a catheter with a hookingelement to withdraw the entire assembly from patient 18 via urethra 20.In still further embodiments, such a loop may be long enough to extendout of the urethra, so that the loop can be grabbed with an externaldevice or the human hand to pull the sensor 12 out of the patient.

FIG. 9 is a cross-sectional side view of distal head 68 of deploymentdevice 66 during deployment and fixation of pressure sensor 12. In theexample of FIG. 9, distal head 68 a vacuum line 78 and a positivepressure line 80. Vacuum line 78 is coupled to vacuum source 74 via atube or lumen extending along the length of sheath 69. Similarly,positive pressure line 80 is coupled to positive pressure source 76 viaa tube or lumen extending along the length of sheath 69. Vacuum line 78is in fluid communication with vacuum cavity 39, and permits thephysician to draw a vacuum and thereby capture a portion 42 of mucosallining 44 within the vacuum cavity. Positive pressure line 80 permitsthe physician to apply a pulse of high pressure fluid, such as a liquidor a gas, to drive fixation pin 46 into sensor housing 26 and throughthe portion 42 of mucosal lining 44. Pin 46 thereby fixes sensor housing26 to mucosal lining 44. In some embodiments, a membrane mounted over anopening of positive pressure line 80 may be punctured by pin 46.

Optical fiber 28 resides within a channel of sheath 69 prior todetachment or sensor 12 from distal head 68. Once fixation pin 46attaches sensor 12 to bladder 24, vacuum line 78 is no longer needed.However, in some embodiments, vacuum line 78 may be used to detachpressure sensor 12 from distal head 68 of deployment device 66. Byterminating vacuum pressure, or briefly applying positive pressurethrough vacuum line 78, for example, head 68 may separate from sensor 12due to the force of the air pressure. In this manner, vacuum line 78 mayaid in detachment of sensor 12 prior to withdrawal of deployment device66.

As described previously in FIG. 3, fixation pin 46 punctures mucosallining 44 for fixation of sensor 12. While the force of this fixationmay vary with patient 18, deployment device 66 provides adequate forcefor delivery of pin 46. In an exemplary embodiment, positive pressureline 80 is completely sealed and filled with a biocompatible fluid, suchas water, saline solution or air. Sealing the end of positive pressureline 80 is a head 82 on fixation pin 46. Head 82 is generally able tomove within positive pressure line 80 much like a piston. Force to pushfixation pin 46 through the portion 42 of mucosal lining 44 captured invacuum cavity 39 is created by application of a pulse of increased fluidpressure within positive pressure line 80. For example, the physicianmay control positive pressure source 76 via control handle 70. Thissimple delivery method may provide high levels of force, allow multiplecurves and bends in articulating arm 306, and enable a positive pressureline 80 of many shapes and sizes.

In an alternative embodiment, a flexible, but generally incompressible,wire may placed within positive pressure line 80 and used to forcefixation pin 46 through the captured portion 42 of mucosal lining 44.This wire presents compressive force from control handle 70 directly tothe head 82 of fixation pin 46. This method may eliminate any safetyrisk of pressurized fluids entering patient 18 or, in some embodiments,permit retraction of pin 46 after an unsuccessful fixation attempt. Theflexible wire may be attached to pin 46 and pulled back to remove thepin from capture mucosal tissue 42. The flexible wire may be shearedfrom fixation pin 46 for detachment purposes as distal head 68 releasessensor 12. This detachment may be facilitated by a shearing element orsimply low shear stress of the wire enables separation when distal head68 slides past pin 46.

In FIG. 9, deployment device 66 illustrates optical fiber 28 on the sameend of housing 26 as sheath 69, while the fixation structures arelocated in the opposite, or distal end of distal head 68. In someembodiments, it may be necessary for pressure sensor 12 to be deployedwith tube section 30 located at the distal end of head 68 and thefixation structures located near sheath 69. In still other embodiments,the fixation structures and tube section 30 may be located on the sameend of pressure sensor 12.

In some embodiments, deployment device 66 may include a small endoscopiccamera in the distal head 68. The camera may enable the physician tobetter guide deployment device 66 through urethra 20, past sphincter 22,and to a desired attachment location of bladder 24 in less time withmore accuracy. Images may be displayed using video fed to a displaymonitor.

FIG. 10 is a cross-sectional bottom view of the deployment device 66 ofFIG. 10 before attachment of pressure sensor 12. As shown in FIG. 10,distal head 68 includes proximal tube channel 84 to accommodate opticalfiber 28 during placement of sensor 12 and distal tube channel 86 toaccommodate the flexible tube during retraction of deployment device 66.In addition, sheath 69 includes a sheath channel 88 to accommodateoptical fiber 28 and flexible tube section 30. Channels 84, 86, 88 serveto retain tube section 30 during delivery of sensor 12 to an attachmentsite. Note that the channels are larger than the shown portion ofoptical fiber 28 to enable the passage of the larger perturbationsection 30 of optical fiber 28. In some embodiments, tube section 30 maybe of similar diameter to optical fiber 28.

Distal head 68 is rounded on both sides at the distal end to permiteasier entry of deployment device into areas of patient 18. Head 68 mayalso be lubricated before delivery to facilitate ease of navigation. Onthe proximal end of head 68, proximal tube channel 84 runs through thehead for unimpeded removal of optical fiber 28 and tube section 30during detachment of pressure sensor 12. This channel may be U-shaped,e.g. closed on 3 sides. In some embodiments, proximal tube channel 84may be an enclosed hole in which optical fiber 28 resides and glidesthrough upon deployment device 30 removal.

Sheath channel 88 is formed within sheath 69 to allow optical fiber 28to stay in place during delivery of pressure sensor 12. In thisembodiment, optical fiber 28 is only partially retained within channel88. In some embodiments, sheath channel 88 may be deeper to allowoptical fiber 28 to lie completely within sheath 69, whereas others mayinclude a completely enclosed channel out of which optical fiber 28glides after attachment.

Distal channel 86 in distal end of head housing 68 is not used byoptical fiber 28 before attachment. The purpose of this open channel isto allow optical fiber 28 and flexible tube section 30 to glide throughit while head 68 is removed from bladder 24. As head 68 slides back pastpressure sensor 12, optical fiber 28 and tube section 30 will slidethrough channel 86 and head housing 68 will keep optical fiber 28 andtube section 30 between the wall of bladder 24 and head 68 until head 68has been removed beyond sphincter 22. Optical fiber 28 and tube section30 may then be ensured correct placing through sphincter 22.

Some embodiments of optical fiber 28 and flexible tube section 30include multiple length and diameter combinations which would lead tomodifications in channels 84, 86 and 88. These channels may be ofdifferent diameters or lengths to properly house optical fiber 28, tubesection 30, or both. One embodiment may include flexible housingchannels to accommodate a wide variety of dimensions. Furtherembodiments of deployment device 30 may contain modified channellocations in head housing 68. These locations may be needed to placeoptical fiber 28 and flexible tube section 30 in different locations,particularly at different sphincter sites as in some embodiments.

FIG. 11 is a flow diagram illustrating a technique for delivery ofstimulation therapy based on closed loop feedback from an implantablepressure sensor. In the example of FIG. 11, implantable stimulator 14requires information from implantable pressure sensor 12 and externalprogrammer 16. The flow of events begins with implantable stimulator 14communicating with implantable pressure sensor 12 and sending a commandto sense the pressure of sphincter 22 (90). The pressure sensor 12subsequently acquires a pressure measurement and delivers the data toimplantable stimulator 14 (92). Upon receiving the pressure data,implantable stimulator 14 calibrates the data and compares it to adetermined minimum pressure threshold (94).

If the measured pressure is higher than the threshold, the loop beginsagain. If the pressure is lower than the threshold, the flow continuesto the next step of stimulation. Implantable stimulator 14 communicateswith external programmer 16 to check if patient 18 has desired to voidthe contents of bladder 24 (96). If patient 18 has signaled a voidingevent, stimulation is skipped and the process begins again. In the caseof no voiding event desired, sphincter 22 is not providing adequateclosing pressure and needs to be stimulated, or more vigorouslystimulated. Implantable stimulator 14 next performs the necessary tasksto adjust a level of stimulation for stimulation pulse generator 60(98). Stimulator 14 concludes the loop by delivering electricstimulation thereby to a nerve that innervates sphincter 22 (100). Afterstimulation therapy has commenced, the loop begins again to continueappropriate therapy to patient 18.

In some embodiments, pressure sensor 12 may be used exclusively formonitoring pressure without providing feedback for stimulation therapy.In this case, the logic loop would be much simpler and only includecollecting data and sending it to an external programmer (90 and 92).Pressure may be measured continuously, intermittently or at the requestof external programmer 16. These embodiments may be used for diseasediagnosis or condition monitoring and may provide a patient to avoidfrequent clinic visits and uncomfortable procedures. In someembodiments, the pressure measurements may form part of an automatedvoiding diary that records voluntary voiding events, involuntary voidingevents, and urinary sphincter and urethral pressure levels prior to,contemporaneous with, of after such an event.

Although the invention may be especially applicable to sensing urinarysphincter pressure, the invention alternatively may be applied moregenerally to other sphincters within the patient, such as the loweresophageal sphincter (LES) or pyloric sphincter. In addition, in thoseinstances, the invention may be adapted to support electricalstimulation of other body organs, such as the stomach or intestines,e.g., for treatment of obesity or gastric mobility disorders. Not onlymay stimulation of certain nerves allow for the proper closure of asphincter, but nerve stimulation may be able to modify stomachcontractions or intestinal contractions based upon pressure measurementsat those sites. Pressure feedback from the implantable pressure sensormay be the most effective therapy for some patients, e.g., in the formof biofeedback that aids the patient in self-regulating bladder control.Also, the invention need not be limited to neurostimulation, and may beapplied to stimulate other tissue, including muscle tissue.

Various embodiments of the described invention may include processorsthat are realized by microprocessors, Application-Specific IntegratedCircuits (ASIC), Field-Programmable Gate Arrays (FPGA), or otherequivalent integrated or discrete logic circuitry. The processor mayalso utilize several different types of data storage media to storecomputer-readable instructions for device operation. These memory andstorage media types may include any form of computer-readable media suchas magnetic or optical tape or disks, solid state volatile ornon-volatile memory, including random access memory (RAM), read onlymemory (ROM), electronically programmable memory (EPROM or EEPROM), orflash memory. Each storage option may be chosen depending on theembodiment of the invention. While the implantable stimulator andimplantable pressure sensor ordinarily will contain permanent memory, apatient or clinician programmer may contain a more portable removablememory type to enable easy data transfer for offline data analysis.

Many embodiments of the invention have been described. Variousmodifications may be made without departing from the scope of theclaims. For example, although the invention has been generally describedin conjunction with implantable neurostimulation devices, a flexibletube sensor may also be used with other implantable medical devices,such as electrical muscle stimulation devices, functional electricalstimulation (FES) devices, and implantable drug delivery devices, eachof which may be configured to treat incontinence or other conditions ordisorders. These and other embodiments are within the scope of thefollowing claims.

1. An implantable electrical stimulation system comprising: animplantable pressure sensor including: an optical fiber, an emitter thattransmits light via the optical fiber, a flexible tube section coupledto the optical fiber, a reflective, flexible diaphragm mounted withinthe flexible tube section, wherein the diaphragm reflects the lighttransmitted via the optical fiber and deflects in response to exertionof pressure against the flexible tube section by a sphincter with apatient, a detector that detects reflected light via the optical fiber,circuitry that generates pressure information based on the detectedlight, and a fixation mechanism that positions the optical fiberproximate the sphincter within the patient; and an implantablestimulator that delivers electrical stimulation to the patient based onthe pressure information.
 2. The system of claim 1, wherein thecircuitry generates the pressure information based on changes in one ormore properties of the reflected light in response to deflection of thediaphragm.
 3. The system of claim 1, wherein the optical fiber includesa first optical fiber that transmits the light from the emitter and asecond optical fiber that receives the light reflected by the diaphragm.4. The system of claim 1, wherein the optical fiber and the flexibletube section have a combined length of less than approximately 7 cm andthe flexible tube section has an outer diameter of approximately 1 to 3mm.
 5. The system of claim 1, wherein the implantable pressure sensorincludes a housing, the optical fiber extends from the housing, and thefixation mechanism is positioned to attach the housing to an inner wallof a bladder of the patient.
 6. The system of claim 1, wherein theimplantable sensor includes a telemetry circuit that transmits thepressure information.
 7. The system of claim 6, wherein the telemetrycircuit transmits the pressure information to the implantablestimulator, and the implantable stimulator adjusts one or moreparameters of the electrical stimulation based on the transmittedpressure information.
 8. The system of claim 6, further comprising anexternal programmer to adjust stimulation parameters associated with theelectrical stimulation delivered by the implantable stimulator, whereinthe telemetry circuit transmits the pressure information to the externalprogrammer.
 9. The system of claim 1, wherein the implantable pressuresensor includes a sensor housing, wherein the optical fiber and flexibletube section extend from the sensor housing, the system furthercomprising a cystoscopic deployment device to deploy the implantablepressure sensor, the deployment device defining a cavity to carry thesensor housing and a channel to accommodate the optical fiber andflexible tube section extending from the housing.
 10. The system ofclaim 1, wherein the implantable stimulator configures the electricalstimulation to modify contraction of the sphincter.
 11. The system ofclaim 1, wherein the implantable stimulator configures the electricalstimulation to alleviate urinary incontinence.
 12. An implantablepressure sensor comprising: an optical fiber; an emitter that transmitslight via the optical fiber; a flexible tube section coupled to theoptical fiber; a reflective, flexible diaphragm mounted within theflexible tube section, wherein the diaphragm reflects the lighttransmitted via the optical fiber; a detector that detects reflectedlight via the optical fiber; circuitry that generates pressureinformation based on the detected light; and a fixation mechanism thatpositions the optical fiber proximate a sphincter within a patient,wherein the diaphragm deflects in response to exertion of pressureagainst the flexible tube section by the sphincter.
 13. The sensor ofclaim 12, wherein the circuitry generates the pressure information basedon changes in one or more properties of the reflected light in responseto deflection of the diaphragm.
 14. The sensor of claim 12, wherein theoptical fiber includes a first optical fiber that transmits the lightfrom the emitter and a second optical fiber that receives the lightreflected by the diaphragm.
 15. The sensor of claim 12, wherein theoptical fiber and the flexible tube section have a combined length ofless than approximately 7 cm and the flexible tube section has an outerdiameter of approximately 1 to 3 mm.
 16. The sensor of claim 12, furthercomprising a sensor housing, the optical fiber extending from thehousing, and the fixation mechanism is positioned to attach the housingto an inner wall of a bladder of the patient.
 17. The sensor of claim12, wherein the implantable sensor includes a telemetry circuit thattransmits the pressure information.
 18. The sensor of claim 12, furthercomprising a sensor housing, wherein the optical fiber extends from thesensor housing, and wherein the fixation mechanism includes a vacuumcavity defined by the sensor housing and a pin that extends throughtissue captured in the vacuum cavity.
 19. An implantable pressure sensorcomprising: a sensor housing; an optical fiber extending from the sensorhousing; a flexible tube section coupled to the optical fiber; areflective, flexible diaphragm within the flexible tube section; anemitter that transmits light via the optical fiber to the diaphragm; adetector that detects reflected light from the diaphragm the opticalfiber; circuitry that generates pressure information based on thedetected light; and a fixation mechanism that positions the opticalfiber proximate a sphincter within a patient, wherein the diaphragmdeflects in response to exertion of pressure against the flexible tubesection by the sphincter.
 20. The sensor of claim 19, wherein theoptical fiber includes a first optical fiber that transmits the lightfrom the emitter and a second optical fiber that receives the lightreflected by the diaphragm.
 21. The sensor of claim 19, wherein theoptical fiber and the flexible tube section have a combined length ofless than approximately 7 cm and the flexible tube section has an outerdiameter of approximately 1 to 3 mm.